#include<bits/stdc++.h>
#define ii pair<int,int>
#define st first
#define nd second
using namespace std;
const int N=10000;
int n,m,q,ans,a[N][N],vis[N][N],kq[N][N];
int dong[]={-1,0,0,1},
cot[]={0,1,-1,0};
void bfs(int x, int y)
{
memset(vis,-1,sizeof(vis));
vis[x][y]=0;
queue<ii>q;
q.push({x,y});
while(!q.empty())
{
ii tmp=q.front();
q.pop();
int u=tmp.st, v=tmp.nd;
for(int k=0;k<4;k++)
{
int c=u+dong[k],
d=v+cot[k];
if (d>0&&d<=m&&c>0&&c<=n&&vis[c][d]==-1)
{
vis[c][d]=vis[u][v]+1;
kq[c][d]=min(kq[c][d],vis[c][d]);
q.push({c,d});
}
}
}
}
int main()
{
ios_base::sync_with_stdio(false);cin.tie(0);
//freopen("DISPERSAL.inp","r",stdin);freopen("DISPERSAL.out","w",stdout);
cin>>n>>m>>q;
for(int i=1;i<=n;i++)
{
for(int j=1;j<=m;j++) kq[i][j]=INT_MAX;
}
for(int x,y,i=1;i<=q;i++)
{
cin>>x>>y;
kq[x][y]=0;
bfs(x,y);
}
int ans=0;
for(int i=1;i<=n;i++)
{
for(int j=1;j<=m;j++) ans=max(ans,kq[i][j]);
}
cout<<ans;
}
